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July 21, 2017

A NEW STUDY from Columbia University highlights some of the challenges airlines will face in the years ahead as climate change causes temperatures to rise worldwide. The report, by doctoral student Ethan Coffel and climatologist Radley Horton was published in the journal Climatic Change. It estimates that up 30 percent of commercial flights will face payload restrictions as heat waves and extreme temperature events become more common. The report comes only a few weeks after a severe heat wave caused the grounding of dozens of flights in the American southwest.

Heat affects planes in different ways. First, there are aerodynamic repercussions. Hotter air is less dense than cooler air, so a wing produces less lift. This is compounded by reduced engine output. Jet engines don’t like low-density air either, and don’t perform as well in hot weather. Together, this means longer takeoff and landing distances. Depending on the airport, the required runway length may or may not be available (you need enough pavement not simply to get off the ground, but enough to come to a stop should anything go awry). Rates of climb are also impeded (performance parameters require that a plane be able to climb away safely and avoid all obstructions following an engine failure). A maximum weight is calculated for every takeoff. Penalties aren’t uncommon in hot weather, whereby a plane isn’t able to accept a full load of passengers or cargo.

In addition, some aircraft have hard temperature limits set by the manufacturer. These limits tend to be quite high, at around 50 degrees C (122 degrees F), but every once in a while it does get that hot, and flights are grounded outright.

You’ve also got the simpler, more tangible complications: overheating electronics, increased brake temperatures, cabin cooling issues, and so on. Airplanes have a lot of internal machinery, and much of it runs hot to begin with. Throw in triple-digit temperatures, and things begin to break down. And let’s not forget the effects on ground support equipment and the people working outside.

Thanks to rising global temperatures, you can expect weight penalties and groundings to become more frequent. Certain areas of the world, and in turn certain airlines and air travel markets, are going to be harder hit than others. It’ll be interesting to see how this impacts the Gulf carriers — Etihad, Qatar Airways, and Emirates — whose hub airports are located in one the world’s hottest regions. Fortunately for them, many of their long-haul flights arrive and depart in the dead of night, when it’s marginally cooler, but they have much to lose if summer temperatures, which already top a hundred degrees routinely, begin getting warmer.

This issue hasn’t been much in the forefront of Boeing’s or Airbus’s thinking, but the world’s plane-makers will have little choice but to design aircraft with better hot-weather performance. It’s a challenge that can be met — albeit one that we shouldn’t have gotten ourselves into in the first place, but that’s another conversation. One big problem, though, is that it takes a long time — the better part of a decade — to design, develop, and produce a new commercial plane. As for existing aircraft, there’s not a lot that can be done. You can’t just slap new wings or new engines onto a plane.

And we haven’t even touched yet on the ways an altered climate is going to intensify wind patterns, storms, and turbulence.

Last spring, a paper out of the U.K. suggested that instances of strong, potentially dangerous turbulence will increase significantly by the middle of the century. The frequency of moderate to severe turbulence encounters is expected to rise as much as 127 percent. You can read more details here. Data collection on routes across the North Atlantic shows things trending this way already, with marked increases in both the severity and frequency of turbulence.

I’ve been flying across the North Atlantic since 1997. My observations are just that, and are purely anecdotal, but what I’ve experienced more or less meshes with the research. It’s become bumpier and windier, on average, and storms seem to be larger and more widespread. It’s no longer uncommon to encounter thunderstorms even in the colder months.

We also can expect an increase in the severity of hail, low-level gusts, windshear and microbursts. More frequent and powerful storms, both in summer and winter, will wreak logistical havoc at airports.

So here we are. This is another way in which we’re ill prepared for the coming challenges of climate change. And the bottom line repercussions for airlines could be in the tens of billions annually.

This subject is a tough one for me. It concerns me as a citizen, but it affects me on a personal level, too, and it leaves me feeling uneasy. I am, after all, an airline pilot.

I’m probably greener than most people, abiding best I can by the three Rs of good stewardship: reduce, reuse, recycle. I don’t own a car. I compost food scraps and recycle almost everything else. Much of the furniture in my apartment was scavenged from curbsides and refurbished by hand. I’ve replaced my incandescent light bulbs with compact fluorescents. But then I go to work and expel hundreds of tons of carbon into the atmosphere. Am I a hypocrite or what?

If I enjoy any consolation, it comes in knowing that commercial aviation’s share of greenhouse gasses remains, at least for now, pretty small. I’m the first to agree that airlines ought to be held accountable for their fair share of ecological impact, but that’s the thing: globally, commercial aviation accounts for only about two percent of all fossil fuel emissions. Commercial buildings, for one, emit a far higher percentage of climate-changing pollutants than commercial planes, yet there is little protest and few efforts to green them up. It’s similar with cars. Americans have staggeringly gluttonous driving habits, yet rarely are we made to feel guilty about them. U.S. airlines have increased fuel efficiency 70 percent over the past thirty years, 35 percent since 2001 alone, mostly through the retirement of fuel-thirsty aircraft. Average fuel efficiency of the American automobile, on the other hand, has stayed stagnant for at least three decades, and if the current political environment is any indication, it’ll be going backwards.

The sticking point, though, is that the true measure of aviation’s environmental impact goes beyond simple percentages. For one thing, aircraft exhaust—containing not only carbon dioxide, but also nitrogen oxides, soot, and sulfate particles—is injected directly into the upper troposphere, where its effects aren’t fully understood. As a rule of thumb, experts recommend multiplying that previously cited two percent fossil fuel figure by another 2.5 to get a more accurate total of the industry’s greenhouse contributions. Using this formula, airlines now account for about five percent of the problem.

That’s still not much, but civil aviation is growing rapidly around the world. China alone is planning to construct over forty large airports. In the United States, the number of annual passengers, already over a billion, is anticipated to double by 2030, at which point greenhouse gases from planes would rise to as much as five times current levels. If indeed we begin reducing the carbon output from other sources, as we keep promising to, the output from aviation will rise drastically as a percentage of the whole.

The reason for all of this growth is that hopping on a plane is relatively cheap and easy. That may change. Air travel will always be an economic necessity, but the kinds of flying we’ve become used to might not always be possible should petroleum prices climb.

Several carriers, meanwhile, are experimenting with biofuel alternatives to jet fuel. Air Canada, Qantas, United, and All Nippon Airways are among those that have operated revenue flights powered completely or partly by biofuel. In the meantime, many airlines allow passengers to purchase inexpensive carbon offsets when booking online. Or, for a small fee, there are third-party organizations that will offset the estimated CO2 of your journey, investing the money in sustainable energy projects.

Now forget emissions for a minute and let’s talk about other kinds of pollution:

One thing that always shocks me is the amount of material waste — namely plastics, paper, Styrofoam, and aluminum — thrown away by airlines and their customers. Take the number of trays, cups, soda cans, snack wrappers, and discarded reading material produced during the average flight, and multiply it by the tens of thousands of daily commercial departures around the world. Simple measures would go a long way toward reducing and reusing. For instance, why not offer passengers the option of receiving a cup with their beverage? My can of soft drink or juice always comes with a cup, dropped onto my tray before I have a chance to say no, even though it would be perfectly acceptable to drink from the container. And the packaging of airline food is nothing if not extravagantly wasteful. The typical inflight meal or snack consists of more petroleum-derived plastic than actual food.

Not all airlines ignore the waste problem. Virgin Atlantic’s onboard recycling program asks passengers to hand in glass bottles and cans and leave newspapers on their seats for recycling. At American Airlines, cans are recycled, with the money going to charity, and trash from domestic flights is separated and recycled. Delta recycles all aluminum, plastic, and paper products from flights into its Atlanta megahub, with proceeds going to Habitat for Humanity. But while a few carriers are stepping forward, the industry-wide effort has, for the most part, been pretty halfhearted.

51 Responses to “Air Travel and the Environment”

Is battery technology ready to power a small regional aircraft? Israeli startup Eviation Aircraft believes it is, and it has selected South Korea’s Kokam to supply lithium polymer batteries to power a full-scale prototype of its Alice nine-passenger, all-electric regional aircraft by early 2019.

According to the documentary “City in the Sky” it takes 17,500 2 liter bottles (think Coca-Cola) of Jet A-1 to fuel the average airliner. It costs $28,000 and takes 30 minutes to fill the tanks of an A-380. Airlines consume $226 Billion dollars of kerosene each year. If you’ve never had a kerosene heater, I can tell you it puts off a lot of carbon. It will blacken your ceiling.

Your characterization of airlines’ GHG emissions of 2.5%-5% as “not much” is troubling. Sure, autos and buildings emit large amounts, perhaps larger amounts than airlines. Not so in the case of rail. That doesn’t mean that 2.5% is insignificant. That’s still a lot, given the overall volume of GHGs emitted–and consequential rising temperatures and sea levels. 5% is 1/20 of total GHGs.

People who take short-hop and medium-distance air trips have alternatives in many cases. Passenger rail is a “green” option for many travelers.

We can (and should) wean ourselves from many air trips if we take vacations nearer home, and use digital tech for meetings. The only practical way to reduce the amount of GHGs produced by planes is to fly less.

The worst environmental abuse by air travelers is the use of private jets (see e.g., Donald Trump’s private 747). Reducing one’s impact on the environment would start with choosing air carries that pack people on a plane. (I’d like to see a comparison of avg CO2 emissions per capita of private jet passengers versus that of commercial airliners.)

Air and auto travel will be with us for the foreseeable future. The US can mitigate a lot of GHGs from these travel modes by building passenger and commuter rail. We’re one of the few industrialized countries not to have this option. We got a long ways to go to be green…

There is one form of transportation when it comes to Greenhouse Gas Emissions that is far worse than even air and auto by a huge landslide: Ships. Cargo and Cruise ships burn what is known as “Bunker Fuel” which are the leftovers of the oil refining process. It’s akin to liquid coal or liquid tar in consistency and environmental pollution, and has to be heated to be burned in the engine. The emissions generated by these ships are so huge that roughly 16 bunker fueled ships make as much pollution as all the combustion powered cars in the world combined, and there are at least hundreds if not thousands of these bunker fuel burning ships in the world’s oceans now running nonstop for days, weeks, and even months. It is so polluting that Europe and most of North America have bunker fuel bans for ships in waters under their control, and they are checked in port to see if they have been following the bans. We are all sunk on climate change unless we put the hammer down on ships and their burning of bunker fuel.

This is an issue very personally troubling to me, given that as a New Zealander I am a minimum of three hours’ flight away from anywhere at all, 12 hours from the US/Hong Kong/Singapore and 26 hours from Europe. That’s a lot of carbon, every single time. It’s dispiriting that airlines are experimenting with biofuel, given that deforestation for biofuel crops creates its own greenhouse gas emissions, not to mention all the other issues biofuel brings along with it including pressure on water resources and the generation of substances like formaldehyde when biofuels are burnt. Back to the drawing board. Please.

New Zealand is roughly at the center of the Water Hemisphere that has the smallest amount of land in it. It also is the closest to the point of the center that has smallest percentage of the global population in a hemisphere. Those geographic barriers and remoteness make boat or flying the only long distance options in New Zealand, and both are extremely carbon spewing too.

You don’t own a car and don’t live in NYC? Patrick, you are remarkable.

Thanks for the excellent piece, chock full of important info. I’m sure we’ll be re-visiting av-enviro a lot in coming years.

I had to really wrack my brains to think of something you didn’t cover. Ah ha! The controversial Eu Carbon Tax Scheme? Bitterly fought by U.S., Chinese and Russian airlines. Congress actually passed a law prohibiting U.S. airlines from paying the tax.

Passing such short-sighted laws will not solve this looming problem.

* * *

The VC-10. Yes, she was elegant, but God was she L-O-U-D-! (outside) I was ship-wrecked on Bermuda and became friends w/folks at the Biological Research Station which sat above the end of the main runway of Kindley Field, now Wade Int’l Airport.

I enjoyed sitting on their porch of an evening, chatting, watching the planes. One night a British Airways VC-10 taxied out. When she lit her 4 pack of Conways to take off, it was like being in a hurricane of noise. See what you think at You Tube’s “Vickers VC-10 awesome airliner! **feel the noise**” That take off is muted by comparison.

I find this piece 23 days after it was posted. So if anyone out there is still reading, I’d like to make name a factor that I don’t find in the post: human overpopulation. Human numbers have more than tripled since my birth, and I’m a relatively modest 62. Set that against the 2 million years (or whatever) of human existence.
Poor old Malthus and the Club of Rome have been the whipping boys of the Growthers for decades now. However, the Growthers’ days are numbered but good. An exponential rise in our numbers will be the death of us, sooner rather than later, and perhaps not such a bad outcome.
Few of the problems Patrick mentions in his article would be problems at all if there were only 500 million of us instead of 7 and a half freaking billion and expanding faster every day.

Agree fully: population is at the root of so many of the planet’s problems, yet is one subject that seems taboo – even among the environmental community.

The fact that an animal population (human included) will, unchecked, grow exponentially whilst availability of raw materials, energy and food supplies can only increase arithmetically should be obvious. And technology has, for a couple of hundred years, enabled the human population to – temporarily – hide that fact.

Look at the way “growth” – or should it be “GROWTH” – is held up to be the be all and end all: it’s ridiculous, and has to be coming to an end if the planet is to sustain itself, although it’s probably too late for that given that we need several earth sized planets even now, let alone in 50 years’ time.

If you examine closely enough, you will realize that every problem on earth is a product of too many humans—from climate change to poverty to species extinction.

Only 400 generations ago (10,000 years) there were only a few million people in the entire world. It was the invention of crop agriculture that allowed the population to increase to present numbers. We now have to cultivate an area the size of South America to provide enough food to feed them.

All modern agriculture and animal production depends on natural systems to exist, as it always must. Yet, world population always increases, making the problem even worse.

Humans will do anything, believe anything and convince themselves of anything to avoid the doing the right thing.

I completely agree. World population has doubled in my lifetime and I’m well under 60. The lonely little 2-lane road my Mom took along the Gulf Coast on the way to the hospital to have me is now not only built up with giant high-rise condos, but they’ve built artificial land out into the bays on the other side of the road and built more high-rise condos there. Pretty much all environmental problems can be traced to there being too bloody many people.

And oddly enough, we give tax breaks to people for having children.

Of course, whenever I bring up the idea of having a per-child tax instead of a per-child tax break, people give me odd looks and sidle away…

Forgive me if this is a dumb question, but…if it was too hot for aircraft to fly from Phoenix during a heatwave, how is it that there is steady air traffic in and out of Dubai, Qatar, etc., where temperatures are considerably higher? Or is it that the heat ban affected mainly smaller regional jets, and the larger, longer range Boeings and Airbuses can handle higher temperatures better (more power and so on)?

Great question. For one thing, yeah, the ban mainly affected certain types of regional jets, which don’t have the performance margins that larger jets do, and/or were up against their manufacturer’s maximum stipulated temp limits. Those Persian Gulf airports also have very long runways.

Don’t forget that Phoenix is a thousand feet elevation! You come up against the WAT limit – weight, altitude and temperature – just because the air temperature is the same at two places it doesn’t mean the performance is equivalent. Higher means lower performance, and when you are right up against the performance limits it’s critical.

Excessive CO2 absorbs and retains solar heat thereby increasing earth’s atmospheric and surface temperatures – all part of the “greenhouse effect”.
CO2 is consumed by vegetation, which emits oxygen. Every bit of destroyed vegetation reduces oxygen production
CO2 is a respiration and combustion product – too many people burning too much coal, gas and oil increases CO2.
Carbon dioxide in sea water will form carbolic acid, thus acidifying the oceans.
For more info search wikipedia for “carbon dioxide”

“Or, for a small fee, there are third-party organizations that will offset the estimated CO2 of your journey, investing the money in sustainable energy projects.”

This. This is one of the big things that grates on me with this whole movement. The false sense of “doing your part” by using the concept of carbon offsets. It’s a total scam and a giant money-making venture. All of this for something that living creatures breathe out as part of their natural function, and green plants “breathe in” for theirs.

CO2 is NOT a pollutant, but the “green” community treats it as one. However, once the false narrative is established, all you need are gullible people to parrot it and ta-da!..you’re off and running, given license to create any absurd program like “carbon offsets” that generates billions for somebody and makes said gullible people feel good about themselves.

While it IS irritating to suggest that people can purchase themselves a clear conscience (bingo — Absolution: No Harm Done), any substance which, when it is pumped into the air, creates potentially catastrophic changes for human life across the planet, is a Pollutant with a capital P.

How refreshing to read a comment by someone who understands biology and earth science. I live near a glacial lake. It was formed about 12,000 years ago when the glaciers that covered what is now my backyard were a mile high and melted due to…wait for it…

GLOBAL WARMING!

That’s right kids, there was global warming long before the Wright Brothers and Henry Ford. It is, normal, natural, expected, etc. As is global cooling. When I was a kid Highlights magazine had a picture of a woolly mammoth on the cover asking “The New Ice Age?”

I don’t even have trash pick-up. I recycle nearly all of my packaging, take big stuff and aluminum to the scrap yard and compost the rest. It just makes sense.

We are fleas on this dog called Earth. We will eventually die and the world will keep turning.

Eric: Water isn’t a pollutant either – but drinking too much of it or diving beneath it for a few minutes makes it into one. And the citizens of Houston would have something to say on that subject (all our sympathies to them.)

Every national science academy in the world has reviewed and agreed the main points of climate change and every single issue that deniers have brought up – again and again – is debunked.

I suggest watching Potholer 54’s excellent YouTube videos as a Climate 101 start. Facts, and facts that can be verified as he gives references to all the evidence and scientific papers.

In case you’re wondering why your new econobox can’t get gas mileage a good as what’s printed on the sticker … it’s complicated. From a footnote to the UCS piece …

The actual Corporate Average Fuel Economy (CAFE) standard is expected to be about 49.6 mpg in 2025, with the remaining 5 miles per gallon equivalent reached through improvements to in-car air conditioners (better efficiency, reduced leaks, and use of refrigerants with a lower impact on the climate). Because CAFE compliance tests are out of date and overinflate fuel economy, the average on-road fuel economy of new cars and light trucks is expected to be 36-37 mpg by 2025. By comparison, the average of today’s on-road fleet is 21 mpg.

It is hard to imagine a 36-37 mpg average without the big boost that comes from hybrids, plug-in hybrids and all-electric cars.

“Captain, today you can take off with 100 passengers to go 4,000 miles or 400 passengers to go 1,000 miles, but it’s just too bloody hot for 400 passengers to go 4,000 miles”

Redesign aircraft systems and engines to cope with higher temperatures, but even then payload and/or range could be economically non-viable.

Alternatively, travel could become more relaxed and civilized with many more ocean liners and high-speed trains. All with lots of air conditioning. Or just hunker down at home or work with 3D VR video conferencing.

Perhaps if the whole world is going to be hotter with less dense air giving less lift, then we should reintroduce the VC10 which was designed for the ‘hot and high’ airports such as Nairobi on the old Imperial routes through East Africa. 🙂

They’d certainly add a bit of class to what has become a very boring looking industry.

Mike, 1962’s VC10 was one of the most elegant jetliners of all time, right up there with Concorde. Like Concorde, the VC10 was a triumph of technology over economics. Only 54 were built, including 13 for the Royal Air Force.
The VC10 ended airline service in 1981. The 13 RAF VC10s, plus 14 ex-airline aircraft, became RAF tankers. They were used until 2013
For lots more info, google “try a little VC-tenderness”

Not to mention the Boeing 757 that was a serious hot and high performer. Boeing though swallowed the low cost carrier bug whole by selling dinky, underpowered, and tinny 737s in mass to them and killed the 757 in arrogant neglect. While the Airbus A320 CEO and NEO certainly have more power and are wider then the 737 NG and MAX, the 757 still has more power than them too. Both the A320 and especially the 737 are going to face sharp weight penalties in the not so distant future.

Gotta agree with Jonny. Love your perspective from the right seat Patrick, but I can’t follow you down this particular rabbit hole.
Scientists can agree on some major climatic points: It is definitely warming..for between 150 to 300 years..the resolution of the proxies isn’t great. And humans are responsible for part of that..largely through land-use changes though CO2 has some effect.
Were climate modelers correct, the the poles would warn more quickly than the tropics . and I don’t think we’re gonna see major lift problems at Nome. In addition since wind and storms depend on energy differentials between Polar and tropical regions it should be expected that major wind events would also be reduced. Which may be why the US has had so little hurricane activity since Katrina.
No reason to trust me…check out Richard Lindzen and Freeman Dyson and the Pielkes father and son. It’s a fascinating area of human ignorance that we don’t yet have the tools to disentangle.
As one of the commenters on a climate site likes to say..that shouldn’t stop us planning..we don’t even plan for the past.

You seem at least reasonable on this topic, which is more than I can say for many people, but it doesn’t matter what you think. It’s happening with or without your consent. And it’ll be interesting to hear the skeptics’ reactions 30 or 40 years from now.

The evolution of excuses has been funny to watch. First, it was that global warming wasn’t happening at all. When that became too silly to maintain, it changed to “Well, it’s happening, but it’s not really people who are causing it.” Now, one that you hear a lot is, “Well, it’s happening, and it’s our fault, but it won’t be as bad as the ‘radical environmentalists’ are saying it will be.”

Actually, if you ask the people who are studying this closely, it’s going to be WORSE. They’re often afraid to say this publicly, because of the backlash that follows, and because the science can’t yet be proven, but what they’re finding is scaring the crap out of many of the scientists.

It’s discouraging, too, how this because a partisan issue. There’s nothing inherently “left” or “right” about it, yet we’ve managed to politicize it. Arguing about HOW TO DEAL WITH IT, maybe, can be a partisan/political conversation, but not the simple existence of it.

My own feeling is that it no longer matters much. We’ve passed the tipping point. We had a twenty or so year window to deal with it, and all we did is make it worse. The mode now should be damage control.

Half a century from now the world is going to be a very different place. Go see a coral reef while you still have the chance.

I myself feel we are well pass the tipping point too, and I am not afraid to say it either. If you want to see where we are rapidly going, look at the Permian Mass Extinction that literally wiped out over 95% of all life on Earth. That is the closest analog we have to our rapidly spiraling and accumulating greenhouse gas emissions we are doing now.

YOU: “My own feeling is that it no longer matters much. We’ve passed the tipping point.”

But, but Patrick: you’re going to put Al Gore out of a job!

Seriously, I’m afraid you’re right. This came home to me when I was sitting in a friend’s garden one evening having drinks. We had a clear view of the southern sky and slowly arose the beautiful white contrail of a 747, side lit by the setting sun.

I began to decry its “clear cutting of the upper atmosphere.” I waxed most eloquent on av-enviro. After I’d finished my lecture, she said, “Well, what should we do?”

“We’ll have to ban them, or course…or fry.”

“Then how would I see my grandkids in California?”

And in that moment, Patrick, I realized that the jig was up. It was over. Florida and Bangladesh would become reefs and all the rest of the doomsday scenario would come. Snow? What’s that?

I think Freeman Dyson is a little beyond…well, a little beyond.

And I’ll be curious to see what that towering intellect Senator James Inhofe of Oklahoma–arch skeptic–has to say. Or our hoax-promoting president. Who or what will they hang all this on?

Patrick, thank you for being a voice of reason. And to those doubting the science, I very much recommend Naomi Oreskes’ work, especially the book Merchants of Doubt. She is a prominent historian of science at Harvard.

Like you I try to make environmental choices in life but do a lot of business travel for work, and it is clear business travel is horrible on the environment. I’d love to be able to pack my sustainable food and drink with me on trips (granted that weight does have to be transported, which is an environmental cost) but TSA and airline weight limits make that difficult or impossible. While traveling I inevitably generate much higher amounts of waste which is bad, even if I recycle as much of it as I can. Everything is in small amounts and requires so much more energy (like daily cleaning of hotel rooms) than living efficiently at home. When possible I use public transport but more often than not the only option is a car rental – I drive EV at home but carbon belcher when on business travel. And so on.

At some point a problem is too large to solve by a few people’s individual action. It can be solved only by large scale collective action, required by government. We are at that point.

Actually, Patrick, the answers are in the paper at the link Speed provided – his numbers include both cars and trucks and futhermore are weighted based on relative sales of cars and trucks.

That’s the good news. The bad news is that the trend really isn’t that good. Your statement about 3 decades is correct. Speed starts by quoting 1975 – which was 42 years ago. The vast majority of the improvement happened during the 70s and early 80s during the energy crisis and the response thereof. Then came Reagan and the “greed is good” revolution and the trend was largely flat until 2006. That’s a long time of little progress. A number of things were happening at around 2006 – widespread recognition of greenhouse gas-caused global warming and high gas prices led to the worst offenders like the Hummer being discontinued. More recently EV and PHEVs combined with large-scale fleet decisions in favor of low polluters has helped. So there has been some improvement in the past 11 years, but your general point isn’t incorrect.

The reason for the big gains early on is pretty simple to explain. Cars went from body on chassis to unibody construction, engines got smaller, throttle body fuel injection instead of carburetors, and more use of lightweight plastics in the interior. Cars were very small and very light. But then in the 1990s cars began to get heavier again, squandering the efficiency gains for safety, performance and comfort. The Tata Bolt, for example, is rated for almost 52 MPG out of a gas engine, but can’t be sold in the US because it won’t pass crash tests. It also doesn’t come with 20 airbags and all the associated electronic paraphernalia that goes along with them. It won’t survive a rollover. But I’m sure it is a safe car. Just not safe enough for American roads (or at least American drivers).